Electroanalytical investigation on the interaction between 6-mercaptopurine and zinc(II), lead(II), and cadmium(II) ions in nonaqueous solvents.

Different electroanalytical techniques have been employed in the study of the interaction between 6-mercaptopurine and zinc(II), lead(II), and cadmium(II) ions in ethanol, dimethylformamide, and dimethylsulfoxide. The stoichiometry of the formed complexes was determined as well as their instability constants. The kinetic parameters of the electrode processes have been also evaluated.

Electroreduction of molybdenum(VI) at a prehydrogenated platinum electrode.

The use of hydrogenated platinum electrodes allows observation of the electroreduction of some oxygenated ions, which is otherwise masked by the reduction of the hydrogen ion. The present paper deals with the reduction of molybdenum(VI) at a prehydrogenated platinum electrode in acid solutions. The experimental conditions for the electrode hydrogenation process are the following: 90 min at a cathodic current density of about 7 A/cm(2) for microelectrodes with an area of 0.02-0.03 cm(2); about 120 min at a current density of 1.5-2 A/cm(2) for microelectrodes with an area of 0.25-0.35 cm(2). The reduction of molybdenum(VI) in 0.8-1.6M H(2)SO(4) occurs in two consecutive steps: the more cathodic wave [Mo(V) to Mo(III)] is for the most part masked by the reduction of the solvent; the less cathodic wave [Mo(VI) to Mo(V)] takes place at E(1 2 ) values of about +0.07 V, is well shaped, diffusion-controlled and usable for the determination of molybdenum down to 4 x 10(-5)M or 6 x 10(-5)M if a rotating disk electrode is used. Interferences from diverse ions have been studied. A generalization of the effect of electrode hydrogenation on the reduction of those oxygenated ions so far studied [i.e., vanadium(IV), uranium(VI) and molybdenum(VI)] is presented.

Electroreduction of uranium (VI) at a platinum electrode and its analytical applications.

Under normal conditions, the reduction of uranium(VI) at a platinum electrode, in acid solutions, is masked by the reduction of the hydrogen ion. If the working electrode is subjected to hydrogen evolution (at a current density of about 7 A cm (2) for 90-120 min) the H(ads) on the platinum surface, acting as a bridge in the electron transfer, shifts the reduction wave of uranium(VI), in 1M sulphuric acid solutions, to potentials (E(1 2 ) congruent with - 0.03 V) less negative than that of the hydrogen discharge (about -0.25 V). The wave corresponding to the reduction of uranium(VI) to uranium(IV) is well shaped, diffusion-controlled, and can be used for the determination of uranium down to 2 x 10(-5)M or 3 x 10(-6)M if a rotating electrode is used. Interferences arise from those ions with similar E(1 2 ) [i.e., Cu(II) and Bi(III)], or from those such as permanganate and dichromate, which oxidize the H(ads) on the platinum electrode. Because of the time required for the electrode pretreatment, the determination is time-consuming but in some respects it appears a useful improvement over the DME.